I-phone amp.

I-Phone Amplifier. A rainy day yesterday, but warm enough to head to the shop/gaarage….but, I needed a project. So, after a little research, I decide to attempt an I-phone amplifier. Four layers of oak, the front and back are 1/4 inch, the second layer is the thickness of the phone and has the sound channels going from the bottom of the phone (where the speakers are) to the “speaker” holes, and the third layer is about 1 inch thick to give depth to the 2 1/4 inch holes. The front three layers are glued up and then hole-sawed out…then the back panel is glued on. The whole box is approx. 4×9 and a bit over 2 inches thick, made from quarter sawn oak and finished with spray poly. A buddy of mine says that there is likely an acoustic “sweet spot” with regard to materials and “speaker” size. If anyone has any info on this, I would appreciate hearing from you. John

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Nice little ‘acoustic amp’! Been planning to do one myself. Cone shaped holes would definitely help I think. I like your oak. Any good hard wood should sound pretty decent I’d think. Maple, cherry, oak etc.

When it comes to a “sweet” spot, you’ll have to do a lot of tinkering. I’ve been getting my feet wet in lutherie, and ever piece of wood (even from the same species and the same tree) resonates differently. A good experiment is to take different thicknesses of different woods and tap them with your knuckle. You’ll quickly hear the different tonal properties of the woods. A general rule of thumb is that the denser the wood, the more “bell-like” the tone. Some of the softer woods (cedar, spruce) vibrate better for stronger amplification (and when the resins harden over the years, they sound even better).

If you are having trouble with amplification at this point, you might want to experiment with thinner pieces. Soundboards for instruments tend to be closer to 3/32”, which allows for a good vibration range. Anything thicker resonates too high (or not at all), anything much thinner gets dull like cardboard…

Perhaps you could try (on another piece, not this one) cutting the large holes straight through; on the back side you could then glue a round piece of thin wood (spruce or cedar is great, but anything would work) and on the front, glue a similar piece (perhaps slightly thinner) with a secondary hole in the middle (so it would resemble a large washer). This would create a sound chamber for resonance and amplification.

I can’t promise it would help anything, but it could be fun to try. It would also allow you to use contrasting woods. If you could perfect the design, there might be a good market for it.

But I was under the impression that you had to make the speaker-holes spherical, to better channel the sounds outward of the speakers? The best way of achieving this, would be to mount the piece on a lathe, and round out the holes like you would, any other bowl.

Follow up.......After making this one prototype, I am convinced there is a lot of room for experimentation. This one works, but now I wonder how much better it could be with some tweaking. To my untrained ear, I feel like the volume is about doubled and the sound is fuller. At this point, I feel like it is working like a megaphone…channeling the sound directionally toward the area in front of the “speaker” holes. I do plan to try making the back panel thinner, to see if the wood resonates more. I can run it through the planer or over the jointer. My “electronics” guy wants to do a few tests for frequency response, pressure, etc….whatever all that means, and we may come up with some new wrinkles on the next generation of this thing.

How about a small Chanel coming up from the bottom and the back that would house the connector for the phone. That way you could plug the phone in and have it in charge mode while you play and listen to music .

The one available from Rocklerhas these dimensions 3-1/2-inch x 8-1/2-inch x 2-inchThe second pic shows the shape that they use (interesting curvature) for sound wave movement in the wood behind the face plate.

Making it from solid cherry appears to give it decent acoustic properties.